The present invention relates to three-dimensional computer graphics generation techniques for generating model data necessary for computer graphics (“CG”) indicative of an actual object for, and more particularly to a method and apparatus for adding coloring information to a solid model. Also, the present invention relates to image processing apparatuses and methods, and more particularly to an image processing apparatus and method that provide higher quality model data necessary for the CC indicative of an actual object.
Along with the recent progress of information technologies, computer-aided image processing is put into active practice, and in particular, image processing technology using the CG has high potential applications to various fields, thus attracting attentions. One conventional method for reproducing an actual object or target using the CO is, as disclosed in Japanese Laid-Open Patent Application No. 2000-348213, a technique to paste actual object images taken by a camera onto various parts of the solid model. This technique prepares many multi-directionally photographed images for various CG's eye points, and selects and paste suitable images, thus generating the CG at the time of reproduction.
However, this method has a disadvantage in that it cannot illuminate the CG-reproduced object with illumination different than that has been used to take its image. As camera images originally include shades and highlights, the object that pastes camera images when provided with additional shades and highlights would become an unnatural image.
Accordingly, as disclosed in “Object Shape and Reflectance Modeling from Observation”, pages 379–387 of SIGRAPH Computer Graphics Proceedings, Annual Conference Series of 1997, one method introduces a function model to handle changes in reflectance due to lighting and eye directions, and to express reflection model constants.
Even comparatively small amount coloring information content would enable natural shades and highlights to be reproduced with an arbitrary illumination condition and an arbitrary eye direction by storing as reflection model constants reflection property of coloring points arranged on a surface of a solid model, and substituting the constants for a reflection model function at a reproduction time. As represented by Phong's reflection model, many reflection models regards a light reflection as a linear sum of a diffuse reflection component and a specular reflection component, each of which is represented by multiple parameters. It is possible to estimate a reflection model parameter by using a set of images taken by changing lighting and eye directions.
Nevertheless, the above reflection model constant is estimated for each coloring point by using a group of images taken by changing lighting and eye directions. Thus, a reproduction of fine designs on the object surface requires reflection model constants to be calculated for coloring points sufficiently densely arranged on the model surface, and to be recorded with the coordinates of the coloring points. Disadvantageously, this would increase coloring information content and cause enormous calculations for estimate and reproduction.
In addition, the conventional methods cannot provide CG images with sufficient shades or highlights, or high quality CG images. For example, a specular reflection component has limited observing directions, and it was difficult to fully measure specular reflections on respective surface parts of the object having various normal directions. Thus, it has been disadvantageous that a specular reflection constant cannot be properly estimated for such parts whose specular reflections are not fully observed. As a result of utmost efforts to this problem, the present inventor has discovered that most of the actual objects often present, even when their base colors delicately change due to patterns and printing, similar materials and surface finishes within a permissible range. In other words, this range presents the same specular reflections, although exhibits different diffuse reflection depending on the base color. In addition, since quality sensation and glossy sensation are perceived in accordance with a state of highlight extent, a difference in specular reflections in a fine area is hard to be perceived.